1. Field of the Invention
The present invention relates to a signal determining apparatus for receiving and amplifying an input signal such as a photocurrent signal and comparing the amplified input signal with a reference voltage.
2. Description of the Related Art
Generally, in a signal determining apparatus, an amplifier circuit is provided to receive and amplify an input signal such as a photocurrent signal to generate an output voltage, and a comparator is provided to compare the output voltage of the amplifier circuit with a reference voltage to generate an output signal. In this case, a response speed of the amplifier is constant (see: JP-2003-139608-A). This will be explained later in detail.
In the above-described prior art signal determining apparatus, when the response speed is relatively low, since a so-called ringing phenomenon such as an overshoot phenomenon or an undershoot phenomenon hardly occurs in the output voltage of the amplifier circuit, spurious waveforms would not appear in the output voltage of the comparator. However, when the response speed is relatively high, since a so-called ringing phenomenon such as an overshoot phenomenon or an undershoot phenomenon occurs in the output voltage of the amplifier circuit, spurious waveforms would appear in the output voltage of the comparator. This would invite a malfunction.